1. Field of the Invention
The invention relates to an improved polishing slurry delivery system for polishing electroless nickel plating used to manufacture hard disk drives. This slurry delivery system is for use with Wittig style machines
2. Description of the Prior Art
Polishing machines for polishing disk drives are known in the art. For example, U.S. Pat. No. 4,930,259 to Kobylenski et al. discloses a Magnetic Disk Substrate Polishing Assembly. In this case, the polishing assembly comprises a polish roller having a continuously fed polish cloth or polish tape. In addition, U.S. Pat. No. 4,845,816 to Nanis discloses a burnishing head for burnishing memory surfaces of computer memory disks.
With regard to the field of the present invention, Seagate Recording Media in Anaheim, California manufactures computer hard drives using a Wittig Polisher. Hans Wittig, of Seagate developed a polisher that is used to planorize or make flat, and polish electroless nickel plating which has been deposited on aluminum substrates This polishing process can be accomplished in two steps. Step one uses a very aggressive polishing process to planorize the nickel plating. Step two involves a less aggressive polishing technique that polishes the nickel to a mirror finish. The resultant substrate has a surface that is flat to within a few millionths of an inch, and has virtually no scratches when viewed with a laser inspection machines. The polishing media is a slurry of very fine aluminum oxide, each particle being less than 0.1 micron in size, and de-ionized water. De-ionized water is corrosive to ferric metals, and will thus cause rapid oxidation to most iron carrying metals.
The Wittig design has one problem in that the slurry and the de-ionized water must travel through more than a total of 20 feet of iron carrying metals per machine to reach the substrate surface. This results in iron oxide (rust) being mixed with the fine slurry and de-ionized water. Since the particles of rust can be several orders of magnitude larger than the very fine particles of the aluminum oxide polishing compound, the rust causes unacceptable scratches in the surface of the substrates.